Due to digitalization and high performance of electronic products, and the like, the needs of consumers have changed. Therefore, market demand is being changed to the development of batteries that are thin, lightweight, and have a high capacity according to a high energy density. Also, in order to address future energy and environment problems, the development of hybrid electric vehicles, electric vehicles, and fuel cell vehicles are actively progressing, and there is a need for a large-sized battery for vehicle power.
As a small and light battery capable of charging and discharging with a high capacity, a lithium-based secondary battery is available, and is used in portable electronic and communication devices such as a small video camera, a mobile phone, and a notebook. The lithium secondary battery includes a cathode, an anode, and an electrolyte. Lithium ions released from a cathode active material are intercalated into an anode active material during charge and desorbed during discharge. Since the ions switch between both electrodes and deliver energy, charge and discharge are possible.
Meanwhile, recently, research on a sodium-based secondary battery using sodium rather than lithium has been in focus again. Since sodium is an abundant resource, when a secondary battery using sodium rather than lithium is manufactured, it may be possible to manufacture the secondary battery at a low cost.
As described above, although the sodium-based secondary battery is beneficial, sodium metal-based secondary batteries in the related art, for example, NAS (Na—S battery) and ZEBRA (Na—NiCl2 battery), are unable to be used at room temperature. That is, there is a problem of battery safety due to use of liquid sodium and a positive electrode active material at high temperatures, and a degradation in battery performance due to corrosion. Meanwhile, recent research on a lithium ion battery using deintercalation of sodium ions has been actively progressing, but an energy density and lifespan characteristic thereof is still low. Accordingly, a sodium-based secondary battery that is able to be used at room temperature and has an excellent energy density and lifespan characteristic is necessary.